One potential solution to mitigate environmental and macroeconomic displacements is the use of energy derived from locally produced biomass. Two particular such bio-fuels are ethanol and biodiesel. While ethanol has garnered more attention due to a longer track record and the activities in Brazil, biodiesel is actually a higher energy fuel with greater environmental benefits. Typically biodiesel is produced by transesterification of triglycerides with methanol.
Most of the production of biodiesel fuel is carried out in batch reactors, where measured quantities of the triglycerides, methanol, and catalyst are added to a tank, heated, and mixed for a period of time ranging from 1 hour to several hours. After a period of time, the reacted mixture is pumped to another vessel and allowed to sit, quiescent for a second period of time. The mixture then phase separates into a biodiesel layer and a glycerol layer, and the glycerol layer is drained. The resulting biodiesel is then further purified.
In some currently used processes, continuous centrifuge technology is used to separate glycerol, and carry out the water washing steps to remove residual alcohol from the biodiesel product. Also, current patent applications include flash separation of methanol from the biodiesel as an alternative method to the water-washing step. Some current processes apply distillation methods to separate the biodiesel from the glycerol byproduct based on their volatility differences. In one current process, biodiesel separation from glycerol is claimed to occur in a reactor where the feed is introduced at the top and an impure biodiesel stream and an impure glycerol stream are both withdrawn near the bottom.
In prior art process, both desired product biodiesel and byproduct glycerol are withdrawn near the bottom of the reactor as liquid streams. The proximity of the withdrawal points for these two product streams implies there will be significant mixing and cross-contamination. This assertion is born out by the presence of many downstream separators and complicated processing required to further purify the products. In this process, the concentration of both products, biodiesel and glycerol, increases towards the bottom of the reactor, thereby hindering the conversion process.
The processes based on reactive distillation produce high purity glycerol and high purity biodiesel with small amounts of residual methanol. However, these processes are energy intensive due to the necessity of providing large quantities of heat to boil the bottoms product and produce the vapor stream for the distillation column. Distillation processes separate materials having different volatility by successively vaporizing higher and higher purity streams of the more volatile material and successively condensing higher and higher purity streams of the less volatile material. This process depends on the equilibrium between vapors and liquids, and is driven by the heat input necessary to boil the material.
Although these processes successfully produce biodiesel fuel, more efficient, economical processes are continuously sought.